linux-kernel - Re: [PATCH 4/9] dt-bindings: Add RISC-V incoming MSI controller bindings

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Date:   Mon, 14 Nov 2022 12:14:19 +0000
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Anup Patel <apatel@...tanamicro.com>
CC:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Atish Patra <atishp@...shpatra.org>,
        Alistair Francis <Alistair.Francis@....com>,
        Anup Patel <anup@...infault.org>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH 4/9] dt-bindings: Add RISC-V incoming MSI controller
 bindings

On Mon, Nov 14, 2022 at 05:36:06PM +0530, Anup Patel wrote:
> On Mon, Nov 14, 2022 at 3:19 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
> >
> > On 11/11/2022 05:42, Anup Patel wrote:
> > > We add DT bindings document for RISC-V incoming MSI controller (IMSIC)
> > > defined by the RISC-V advanced interrupt architecture (AIA) specification.
> > >
> > > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > > ---
> > >  .../interrupt-controller/riscv,imsic.yaml     | 174 ++++++++++++++++++
> > >  1 file changed, 174 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/riscv,imsic.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/interrupt-controller/riscv,imsic.yaml b/Documentation/devicetree/bindings/interrupt-controller/riscv,imsic.yaml
> > > new file mode 100644
> > > index 000000000000..05106eb1955e
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/interrupt-controller/riscv,imsic.yaml
> > > @@ -0,0 +1,174 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/interrupt-controller/riscv,imsic.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: RISC-V Incoming MSI Controller (IMSIC)
> > > +
> > > +maintainers:
> > > +  - Anup Patel <anup@...infault.org>
> > > +
> > > +description:
> > > +  The RISC-V advanced interrupt architecture (AIA) defines a per-CPU incoming
> > > +  MSI controller (IMSIC) for handling MSIs in a RISC-V platform. The RISC-V
> > > +  AIA specification can be found at https://github.com/riscv/riscv-aia.
> > > +
> > > +  The IMSIC is a per-CPU (or per-HART) device with separate interrupt file
> > > +  for each privilege level (machine or supervisor). The configuration of
> > > +  a IMSIC interrupt file is done using AIA CSRs and it also has a 4KB MMIO
> > > +  space to receive MSIs from devices. Each IMSIC interrupt file supports a
> > > +  fixed number of interrupt identities (to distinguish MSIs from devices)
> > > +  which is same for given privilege level across CPUs (or HARTs).
> > > +
> > > +  The arrangement of IMSIC interrupt files in MMIO space of a RISC-V platform
> > > +  follows a particular scheme defined by the RISC-V AIA specification. A IMSIC
> > > +  group is a set of IMSIC interrupt files co-located in MMIO space and we can
> > > +  have multiple IMSIC groups (i.e. clusters, sockets, chiplets, etc) in a
> > > +  RISC-V platform. The MSI target address of a IMSIC interrupt file at given
> > > +  privilege level (machine or supervisor) encodes group index, HART index,
> > > +  and guest index (shown below).
> > > +
> > > +  XLEN-1           >=24                                 12    0
> > > +  |                  |                                  |     |
> > > +  -------------------------------------------------------------
> > > +  |xxxxxx|Group Index|xxxxxxxxxxx|HART Index|Guest Index|  0  |
> > > +  -------------------------------------------------------------
> > > +
> > > +  The device tree of a RISC-V platform will have one IMSIC device tree node
> > > +  for each privilege level (machine or supervisor) which collectively describe
> > > +  IMSIC interrupt files at that privilege level across CPUs (or HARTs).
> > > +
> > > +allOf:
> > > +  - $ref: /schemas/interrupt-controller.yaml#
> > > +
> > > +properties:
> > > +  compatible:
> > > +    items:
> > > +      - enum:
> > > +          - vendor,chip-imsics
> >
> > There is no such vendor... As Conor pointed out, this does not look
> > correct. Compatibles must be real and specific.
> 
> Previously, Rob had suggest to:
> 1) Mandate two compatible strings: one for implementation and
>     and second for specification
> 2) Since this is new specification with QEMU being the only
>     implementation, we add "vendor,chip-imsics" as dummy
>     implementation specific string for DT schema checkers
>     to pass the examples. Once we have an actual implementation,
>    we will replace this dummy string.
> 
> Refer, https://www.spinics.net/lists/devicetree/msg442720.html

AFAIU, <vendor> and <chip> are wildcards and do not have the same
meaning as vendor & chip. That's going off of the dt submitting patches
doc though and I don't know if the tooling supports this.